It is known to protect an electromagnetic load from incorrect polarity of the operating voltage supplied to it by inserting protective diodes into the collector circuit of the transistor that switches the load on and off. This has the disadvantage, however, that the voltage available to the load is diminished by the amount of the diode voltage. It is also known to protect the electromagnetic load from an incorrect supply voltage polarity by using an actively controlled free-wheeling circuit. This necessitates great expense for components, however, as well as exact triggering of the transistor that switches the load on and off and of the transistor that switches the free-wheeling circuit on and off. Problems also arise in the above-described systems with the heat losses that occur in the protective arrangements, especially with high values of inductance of the electromagnetic load.